Electric circuit interrupter and separable contacts therefor



Jan. 28, 1936. KNEA'SS L 2,029,028

ELECTRiC CIRCUIT INTERRUPTER AND SEPARABLE CONTACTS THEREFOR Filed Feb. 15, 1934 4 Sheets-Sheet l INVENTORS W; M

2&2- ATTORNEY.

Jan. 28, 1936. K E ETAL 2,029,028

ELECTRIC CIRCUIT INTERRUPTER AND SEPARABLE CONTACTS THEREFOR Filed Feb. 15, 1934 4 Sheets-Sheet 2 I N V EN TOR-S #14 A TTORNEY.

Jan. 28, 1936. E, KNEASS 5 AL 2,029,028

ELECTRIC CIRCUIT INTERRUPTER AND SEPARABLE CONTACTS THEREFOR Filed Feb. 15, 1934 4 Sheets-Sheet 3 Jan. 28, 1936.

ELECTRIC E. KNEASS ET AL 9,28 CIRCUIT INTERRUPTER AND SEPARABLE CONTACTS THEREFOR Filed Feb. 15, 1954 4 Sheets-Sheet 4 INVENTORJ ATTORNEY.

. the arrangements of the prior art Patented Jan. 28, 1936 PATENT OFFICE 2,029,028 ELECTRIC CIRCUIT INTERRUPTER AND SEPARABLE Edwards Kneass and Otto Jensen, asaignors to I-T-E Circuit Breaker Com- CONTACTS THEREFOR Philadelphia,

pany, Philadelphia, Pa., in, corporation of New Jersey Application February 15, 1934, Serial No. 711,315

20 Claims.

Our invention relates to electric circuit interrupters and more particularly to new and im-= proved separable contacts therefor. While our invention is of general application, it is particularly suitable for use with circuit interrupters oi the type known in the art as disconnecting switches.

In the art of electric circuit interrupters, it'ie well known that if the cooperating separable con= tacts are rigid metallic elements, any appreciable misalignment between the contact surfaces, due to inaccuracies or inanufacturinc or assembly, or due to wear or other unforeseen causes, results in unequal pressure distribution throughout the contact surfaces and, in extreme conditions, in singlemoint contact. Among well-known con sequences of faulty contacts is localized over heating which may result in welding of the con tccts.

has been proposed heretofore to avoid the abovementioned difiiculties by the use of resilient current-carrying elements, preferably comprising a plurality of independent strips or laininations, each of which adjusts itself to surface ir= regularities of a cooperating rigid contact ele= meat. It has also been proposed to utilize coop crating rigid contact elements, one of which is mounted with limited freedom or? motion so that it may adjust itself to any irregularities of the stationary contact element, and connecting the flexibly mounted rigid element with external circuit terminals through flexible conducting leads or pigtails. However, both of these arrangements of the prior art have their attendant dis advantages. In the case oi the resilient currentcarrying elements, excess .currents occasioned by heavy overloads or short-circuits, may raise the temperature or the elements to such a point that they lose their resilience. On the other hand, the flexible leads utilized with cooperating rigid elements tend to fail by fatigue when subjected to frequent operation over a perioclof time.

It is an object of our invention, therefore, to overcome the above-mentioned disadvantages oi and to provide a new and improved electric and separable contacts therefor which is simple, reliable and flexible in operation, rugged in structure and economical to manufacture.

It is another object of our invention to provide new and improved separable contacts for-an electric circuit interrupter which are provided with a plurality of points of engagement andin' which equal contact pressures are maintaine'diat these several points of engagement,

circuit interrupter It is another object of our invention to provide new and improved separable contacts for an electric circuit interrupter which are substantial- 1y unaffected by high temperature operation ocoasioned by short-circuits or substantial overloads in a circuit in which the interrupter is connected.

It is a further object of our invention to provide new and improved separable contacts for an electric circuit interrupter in which there are included no flexible or resilient current-carrying elem nts, but in which current is carried entirely between rigid conducting elements.

it still further object of our invention to provide new and improved separable contacts for an electric circuit interrupter which shall be sub= s antielly unaffected by misalignment the co" contacts. .i'... accordance with our invention in its broadest aspects, an electric circuit interrupter is provided with a pair of cooperating contact elements nor maily symmetrical about a common plane, but subject to appreciable misalignment occasioned. by manufacturing or assembly inaccuracies. Each of the contact elements is provided with epposed contact surfaces and there are provided also a pair of rigid conducting bridging elements or contact members, theelen'ients or members being disposed to-engage opposing surfaces of said contact elements in circuit-closing position oi the interrupter. A biasing sprint; forces the bridging elements into engagement with the opposing surfaces of the contact elements to ensure adequate and equal contact pressures at the several points of contact. In certain instances, it may be desirable to utilize a plurality of pairs of bridging elements or contact members, in which case We prefer to exert the spring pressure upon the bridging elements through an equalizing linlz.

For a better understanding of our invention,

together with other and further objects thereof,

reference is had to the following description taken in connection with the accompanying drawlugs, and its scope will be pointed out in the appended clairns.

Referring now to the drawings, Fig. illustrates in elevation an embodiment of our invention in an electric disconnecting switch of the truc l:-= panel type, while Fig. 2 is a plan view oi ,the same apparatus;

Fig. 3 is a detailed perspective of the improved cooperating contact elements utilized in Figs. 1 and 2, while Figs. 4, 5 and 6 show several details of the contact assembly of Fig. 3;

Figs. 7 and 8 represent the improved contact aoaaoas are often subjected to appreciable misalignment due to inaccuracies of manufacture or assembly, or to irregularities in wearing of the contact surfaces, or other causes. These misalignments may be transverse in parallel planes, or may be of the nature of a relative angular rotation between the cooperating contact elements, or a combination of the two. By the term "appreciable misalignment" we refer, throughout this specified tion and the appended claims, to any such misalignment, either transverse or angular, as would substantially interfere with the quality of electrical contact between two rigid cooperating contact elements; it, of course, being clearly understood that extremely minute degrees of misalignment may produce very substantial detrimental eifects on the conductance between the two rigid contact elements.

moved transversel but parallel to the axial plane of the contact element 20. Under these conditions, it is seen that the bridging elements 21 rotate about the pivot pins 26 in a counter-clockwise direction, maintaining substantially equal contact pressures, however, at the points of engagement of their contact surfaces with the opposed contact surfaces of the elements l0 and 20.

This results from the fact that the bridging elements 21 are provided with upper'and lower arcuate contact surfaces which, in effect, roll along the opposed contact surfaces of the elements ill and as they are moved transversely with respect to each other.

The conditions resulting from an angular misalignment of the contact elements it) and 20 are shown in Fig. 8 in which the line aa represents the trace of the common plane of symmetry of the two contact elements when in proper alignment, while the line b-b represents the trace of the plane of symmetry of the upper contact i0 when subjected to an appreciable angular misalignment. Under these conditions, the yoke members 36 and adjust themselves to the positions indicated, allowing the two pairs of opposed bridging elements to take up different angular positions. Due to the knife edge or equivalent contact between the yokes 34 and 35 of the bridging elements 21, the pressure of the biaslng sprin 32 is substantially equalized between the several bridging elements'to maintain equal contact pressures of the several points of contact. If desired, the inner edges of the bridging elements'may be made slightly convex to improve the contact conditions upon an angular misalignment of the contact elements.

Referring more particularly to Fig. 7, it is seen that each of the bridging elements 21 has its movement toward the plane of symmetry of the terminal 20 limited by the projecting tongue 23 and the stop surfaces 40. When the contact assembly is made up of a plurality of groups of opposing bridging elements 2? as, for example, shown in Fig. 1, it is possible, under certain conditions, upon the disengagement of the contact elements it and 26, for adjacent groups of bridging elements to take positions on opposite sides of the plane of symmetry oi the stationary contact iii. In order substantially to avoid such a condition, which would render dimcult the entry of the tongue 22 of the contact element ill between the groups of opposing bridging elements,

the aligning pins are inserted in the upper holes 28 of the bridging elements 21 to maintain the adjacent groups of these elements in approximate alignment: A loose fit is provided for these pins in the holes 29. Upon the disengagement of the stationary and movable contact elements II and 20, the bridging elements 21 are stable in any position of misalignment, either transverse or angular. Thus, when utilised in a truck-type disconnecting switch, as shown in Figs. 1 and 2, the reengagement of the contact elements is facilitated, since the bridging elements-21 remain in the particular condition of misalignment obtaining upon the'separation of the contact elements.

The biasing spring 22 and associated link preferably engage the bridging elements 21 between their points of engagement at the stop surfaces and the tongue 23. With such an arrangevment, upon the disengagement of the contact ele- In Fig. 7 are depicted the conditions resulting":

from a transverse misalignment; that is, when the axial plane of the contact element '0 is" j;ments,-the pivot pins 28 and aligning pins 20 may be removed and the biasing spring 32 and link 28 will maintain the bridging elements in position. Any faulty group of bridging elements 21 may then be removed, by simply pinching together their upper ends, without disturbing the remaining bridging elements. In brief, any particular group of elements may be replaced or repaired .without completely disassembling the whole contact unit.

In Fig. 915 illustrated a modified form of our improved cooperating contacts in which the contact element 20 is replaced by a contact element 20' having an extending tongue 23' provided with opposed cylindrical projections H or projections having at least two segmental cylindrical surfaces. The rigid conducting bridging elements 21 are, in this instance, replaced by the elements 21' which are similar except for the fact that the pivotal hole in one end of each is replaced by recesses 42 registering with one of the projections ll of the contact element 20'. The sides of the recesses 42 comprise plane surfaces disposed at an angle to each other so that when contact is made with the-cylindrical projections 4|, substantially line contacts are formed between each of the plane surfaces and the cylindrical surface tangent thereto.

In this ins ance, the biasing spring 32, together with its associated link 33 and yokes 34 and 35, are disposed nearer the upper contact surfaces of the bridging elements 2? than the lower contact surfaces, for reasons pointed out hereinafter. In this arrangement, also, the slos 36 and 3? in the link 33 are preferably of such dimensions as to limit the outward movement of the opposing bridging elements 2? when engaging the contact surfaces of the projection 22 of the element it), so that the recesses 52 will not clear the projections at when subjected to the longitudinal thrust of engagement or disengagement. In this way the elements 21' are efl'ectively locked to the contact element 20' and may not be withdrawn by sticking or slight welding oi the contact surfaces of the contact element ill and the contact surfaces of the bridging elements 21'.

The particular form of the recesses 42 and the projections 4|, described above, are effective to increase the contact pressures at the contact element 20'. This may be understood more readily by reference to Fig. 10, which constitutes a force diagram at the con act surfaces. Considering perfectly rigid contact surfaces, so that friction may be neglected, the contact pressures at the points of contact are normal to the plane of contact; that is, normal to the plane surfaces constituting the sides of the recesses 42. The force acting at one of these points of contact is represented by the vector N. In this same figure the vector? represents the force applied by the biasing spring 32 at the lower contact sur=- they are not ideally rigid, with the result that there is a slight deformation at the contact surfaces resulting in an'infinitesimal sliding of the surfaces which introduces the element of friction. In the lower portion of the diagram of Fig. 10, the vector F represents the reacting frictional force and is equal to the normal pressure times the tangent of the angle c, which corresponds to the coefficient of friction and is determined solely by the properties of the contact surfaces. Under these circumstances, the vectordvl represents the actual contact pressure between thecontact surfaces, which is somewhat less than the force Nin the ideal case. ditlons will obtain at the upper contact surface of Fig. 10, rather than the ideal conditions de= scribed above. The two opposing forces have the effect of raising or lowering the recesses 62 relative to the projections it to secure equalize tion of the pressures at the two points of con= tact.

With the design of the contact just described, the arithmetical sum of the contact pressures at the two contact surfaces of each projection ii and its registering recess 52 is greater than the applied force F and, therefore, the current-car rying capacity between the two elements, which is a function of the contact pressure, is thereby increased. Since the rating of. the circuit in terrupter, of which the above-described contact elements form a part, is limited by that contact surface having the lowest current-carrying capacity, to secure an equalization of the currentcarrying capacities of the contact elements of Fig. 9, the biasing spring 32 is moved away from the recesses s2 beyond the midpoint between the contact surfaces of the bridging elements El so that the applied force at the upper contact surfaces, as referred to in Fig. 9, is greater than that applied to the lower contact P, which have the amplifying eflect described above. It will be readily apparent that the full cylindrical surfaces 8i, as shown in Fig. 9, and the segmental cylindrical surfaces of Fig. 10 are full equivalents and may be selected as desired. It will also be readily apparent that the cylindrical projections and angular recesses may be replaced by cylindrical projections on. the bridging elements fl and cooperating recesses in the contact element 2d.

, Figs. 11 and 12 are fragmentary views in ele= vationand plan, respectively, of a modified form of the truck type electric disconnecting switch shown in Figs. 1 and 2. In this case, the station ary contacts ill and ii mounted on the insulating supporting panel 88 are, in all respects, similar to those of Fig. 1. In this case, however, the circuit breaker represented schematically at it, in Fig. l, is replaced by a rigid bridging member Obviously, these conaoaaoaa 88 including two distinct contact elements or a single continuous contact element, as illustrated, and having opposed contact surfaces analogous to those of the contact elements of the assemblies so and El of Fig. l. Theconducting blade or member 53 is pivoted at 46 in a suitable frame supported from the insulating panel l6 and is adapted to be operated into circuit-opening and circuit-closing positions either manually or autotically, as desired, by any suitable mechanism indicated schematically as a linkage mechanism 35. In this case the bridging elements 27 of Fig. 3 are replaced by a modified form of bridging elements 36, it and ill which are essentially elements having both ends similar to the upper ends of elements 2?, as shown in Fig. 3. The uppermost bridging elements 36 of Fig. 11 are similar to the others except for the fact that they extend beyond the bridging elements 56 cooperating with the same stationary contact element is and may be composed of any suitable low resistance arc-resistant material, so that the contact is broken at the elements 58' rather than at 66, thus minimizing arcing and its effects at the contact elements at, which are of conducting material of minimum resistance.

The bridging elements it and 56' are loosely pivoted on the pins 68 carried by inwardly extending projections as of brackets 5t secured to the insulating panel it. A pair of biasing springs and associated linkage mechanisms are provided for each two pairs of opposed bridging elements, one on each side of the supporting panel it.

In this modlfication,-which comprises a combined circuit breaker and disconnecting switch, the circuit is completed between the stationary contact elements it and i i with a minimum number of cooperating contact surfaces in series. For example, in the arrangement of Fig. l, in the path between the contact elements it and it are included the contact surfaces of the elements it: the contact surfaces of. the elements 28; the two contact surfaces of the bridging circuit breaker W; the contact surfaces of the elements 25, and the contact surfaces of the elements it. In the arrangement of Figs. ii. and 12, however, the contact surfaces of the elements as, 2i and the bridging circuit breaker ll are combined into the contact surfaces between the bridging elements 6t, til and ii and the rigid bridging member 68, thus eliminating two groups of contacts in series.

While we have illustrated our invention as embodied in electric circuit interrupters employing two or four pairs of rigid conducting bridging elements between cooperating contact elements, it will be obvious to those skilled in th art that any desired number of. such bridging elements may be employed in accordance with the currentcag requirements of the interrupter of which they form a part, and that while we have illustrated our invention as applied to a 3-pole circuit interrupter, it is equally applicable to electric switches or interrupters of any number of poles.

While we have described what we at present consider the preferred embodiment of our invention, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from the spirit of our invention; and we, therefore, aim in the appended claims, to cover all such changes and modifications as fall within the true spirit and scope of our invention,

What we claim is:

1. In an electric switch relatively movable intermediate the ends thereof.and in spaced relation from said conducting member and said other, of said movable contact structures when in said circuit closing position for biasing said bridging elements into engagement with said other of said movable contact structures and into wiping androlling engagement with said conducting member.

2. In an electric switch, contact structure com-- prising bridging elements, mounting means providing independent limited freedom of. movement for each of said elements, a conducting member disposed between said bridging elements and provided with contact surfaces independent of said mounting means arranged to be engaged by the corresponding bridging elements, said elements being movable toward and into engagement with each other intermediate the ends thereof, said elements having recesses opposite their region of engagement, rigid means operatively engaging said elements in said recesses, a spring cooperating with said rigid means for biasing said elements toward each otherand for biasing said elements into rolling and wiping engagement with said conducting member, and a contact positioned between said elements in the closed circuit position, said spring also biasing said elements into engagement with said last named contact.

3. In an electric circuit breaker, contact structure comprising a conductor having contact surfaces, contact elements having contact surfaces disposed for engagement with said surfaces of said conductor, means for mounting said elements on said conductor for their individual limited freedom of movement with respect to said conductor and for conduction of the current through the circuit breaker by said elements substantially independently of said mounting means, a contact arranged to be engaged by said contact elements in the closed circuit position of the circuit breaker, and means resiliently biasing said contact elements into wiping engagement with said contact, said resilient means also biasing said contact elements into wiping engagement with said conductor.

4. In an electric switch, contact structures relatively movable and either of them subject to appreciable departure from a predetermined path, one of said structures comprising bridging elements, means providing a loose pivotal mounting for each of said elements, a conducting member disposed between said bridging elements and provided with contact surfaces independent of' said pivotal mounting and arranged to be engaged by the corresponding bridging elements, another of said movable contact structures posi tioned between said bridging elements in the closed circuit position, each of said elements upon departure of said other of said movable contact structures from a predetermined pathibeing movable on said pivotalmounting to a new position determined by the extent and direction of said departure, and means for retaining saidelements in said new position comprising portions thereof coming into engagement with each other as said other of said movable contact structures moves to open circuit position, and a spring for biasing said portions of said elements into said engagement and for biasing said elements into engagement with said other of saidmovable contact structures and into wiping and rolling engagement with said conducting member.

5. In an electric switch, a contact structure comprising a plurality of pairs of similar bridging laminations, mounting means providing inde-' with one of said opposed surfaces and the opposite free end of said link extending substantially at right angles to said laminations and be-' yond those laminations in engagement with the other of said opposed surfaces, a spring external to said bridging laminations and operatively associated with the said free end of said link for biasing all of said bridging laminations into wiping engagement with said second contact and into wiping and rolling contact engagement with -said conducting member.

6. In an electric switch, contact structure comprising a plurality of bridging elements, means providing a loose pivotal mounting for each of said elements for a limited freedom of movement of each of said elements, a conducting member disposed between said bridging elements and provided with contact surfaces independent of said pivotal mounting arranged to be engaged by corresponding bridging elements, a second contact provided with contact surfaces arranged to be engaged by bridging elements in the closed circuit position, resilient means including equalizing means for biasing said elements substantially equally irrespective of the position of each element within its limited freedom of movement into wiping contact with said second contact and into wiping engagement with said conducting member.

7. In an electrical apparatus, two axially aligned contact members each having two opposed contact surfaces en the outer surfaces thereof, four rigid bridging elements, the first two of said elements engaging corresponding surfaces of each of said contact members and the second two of said elements engaging the opposite corresponding surfaces, and equalizing means including a spring for producing equal bias on each of said rigid elements in a direction to maintain said elements in pressure-engagement with said contact members.

8. In an electric switch, a pair of cooperating relatively movable contact elements normally symmetrical about their plane of relative motion but subject to appreciablemisalignment therefrom, each of said elements having opposed contact surfaces, a plurality of pairs of rigid conducting bridging elements symmetrically supported from one of said contact elements with independent limited freedom of movement, the elements of each pair being disposed to engage opposing surfaces of said contact elements in circuit-closing position of said switch, spring means directly interconnecting the bridging elements for biasing the same into said engagement,

. corresponding to that of the contact elements upon their operation to circuit-opening 1 9. In an electric switch, a pair or cooperating contact elements, a similarly disposed pair of rigid conducting bridging elements for interconnecting said contact elements in circuit-clog position of said switch, a spring disposed to bias said bridging elements into engagement with said contact elements, and an equalizing yoke interposed between said spring and said bridging ele= ments for procuring substantially equal contact pressures at all points of contact.

10. In an electric switch, a pair of cooperating contact elements each having opposed contact surfaces, a plurality of pairs of rigid conducting bridging elements, the elements of each pair being disposed to engage opposing surfaces or said contact elements in circuit-closing position of said switch, spring means disposed to bias said bridging elements into said engagement, and equalizing yokes interposed between said spring means and corresponding bridging elements of said pairs for procuring an equal bias on each or said bridging elements thereby to insure substantial contact pressures at all points of contact.

11. In an electric switch, a pair of cooperating contact elements normally symmetrical about a common plane but subject to appreciable misalignment, each of said elements having opposed contact surfaces, a plurality of pairs of rigid conducting bridging elements, the elements of each pair being disposed to engage opposing surfaces of saidcontact elements in circuit-closing pcsi= tion of said switch, and. means for biasing said bridging elements into engagement with said con= tact elements comprising a link member inter-= posed between said pairs of bridging elements, a pair of yoke members each eng corresponding elements oi said pairs and supported by said linkmember, and a spring threaded on said link and biasing said yokes toward each other, whereby equal bias is applied to all bridging elements thereby to insure substantial contact pressures at all points of contact between said brig elements and said contact elements. a

12. In an electric switch, a pair of cooperating contact elements each having opposed contact surfaces, a pair of rigid conducting bridging ele merits disposed engage opposing surfaces of said contact elements in circuit-closing position of the switch, the contact surfaces of one end of each of said bridging elements and its associated contact element comprising complementary projections and recesses, means for biasing said bridging elements into engagement. and stop mechanism eflective to limit the motion of said bridging elements against the force of said biasing means to an amount insufficient for the detach= ment of said bridging elements from said contact element when the switch is in an operative position but suficient for such detachment when in an inoperative position.

13. In an electric circuit interrupter comprising a pair of stationary contact elements, a mov= able contact assembly comprising a supporting panel and a bridging member movable relative thereto, said bridging member including a pair of contact elements complementary to said sta= tionary contact elements, corresponding station aocaoce I I cry and movable contact elements being normally symmetrical about their plane of relative motion but subject to appreciable misalignment, each of said contact elements having opposed contact surfaces, a pair of rigid conducting bridging elements associatedwith each stationary contact alignment, each of said elements having opposed contact surfaces, a pair of pivot pins removably supported from one oi said contact elements, a plurality of pairs of rigid conducting bridging elements, corresponding elements of said pairs being similarly and loosely pivoted on one of said pivot pins and the elements of each pair being disposed to engage opposing surfaces of said contact elements in circuit closing position of said switch, and means individually for biasing the bridging elements into said engagement, said bridging elements having complementary stop surfaces cooperating with said biasing means to retain said elements 7 in frictional engagement with the contact element on which they are pivoted upon removal of said pivot pins, whereby the bridging elements may be removed in groups without disturbing the remaining elements or the assembly.

15. In an electric circuit breaker, relatively movable contact structure comprising a pair oi contact members, means providing a loose pivotal mounting for each of said members, a movable contact arranged to be engaged at opposite sides thereof by said contact members in the closed circuit position, and means resiliently biasing said members into contact engagement with said movable contact, said contact members likewise biased into contact engagement in the closed circuit position with stationary conducting means independently of said pivotal mounting.

16. In an electric circuit breaker, relatively movable contact structure comprising a pair of contact members, means providing a loose pivotal mounting for each of said members, a stationary conducting member disposed between said contact members and provided with contact surfaces independent of said pivotal mounting arranged to be engaged by the corresponding contact members, a movable contact positioned between said contact members in the closed circuit position, and means resiliently biasing said contact members into engagement with said movable contact, said resilient means likewise biasing said contact members in the closed circuit position into combined rolling and wiping contact engagement with said stationary conducting member.

17. In an electric circuit breaker, relatively movable contact structure comprising a pair of contact members, means including a pair of pins providing a loose pivotal mounting for each of said members, a conducting member to which said pins are secured, said conducting member and said contact members having coacting conacting contact surfaces into direct engagement in said closed circuit position by reason of the aforesaid loose pivotal mounting.

18. In an electric circuit breaker, relatively movable contact structure comprising a stationary conducting member, a pair 0! contact members, means depending from opposite sides oi said conducting member forming pivotal supports for said contact members, said contact members being in direct contact engagement with said conducting member in the closed circuit position, and a movable contact positioned between said contact members in said closed circuit position.

19. In an electric circuit breaker, relatively movable contact structure comprising a stationary conducting member, a plurality of pairs of oppositely disposed contact members pivotally mounted with respect to said conducting member, said contact members arranged to be in direct contact engagement with said conducting member in the closed circuit position independently of the pivotal mountings thereof, a movable conducting blade positioned between said contact members in the closed circuit position so that each side of said blade is engaged by a plurality of contact members, and means including a spring and a member common to a pair of coacting contact members for biasing said contact members individually into equalized contact engagement with said blade and into direct contact engagement with said conducting member.

20. In an electric circuit breaker, relatively movable contact structure comprising a pair at finger contact members, a relatively fixed conducting member, means loosely mounting said contact members for pivotal movement with respect to said conducting member, a movable contact positioned between said finger contact members in the closed circuit position, said finger contact members and said conducting member having coacting contact surfaces independent 0! said pivotal mounting arranged for combined rolling and wiping engagement, and resilient means for biasing said finger contact members into engagement with said movable contact and said conducting member.

EDWARDS KNEASS. OTTO JENSEN. 

